Electrophoresis has been and continues to be a dominant analytical separation technique in the biological sciences. This is because electrophoresis is particularly well suited for biopolymers, e.g. DNA, proteins, carbohydrates, and the like, which are typically of high molecular weight, water soluble, labile and charged. Modern applications of gel electrophoresis range from the molecular weight determination of proteins, e.g. Hames et al. eds., Gel Electrophoresis of Proteins, IRL Press, Washington, D.C.(1984), to DNA sequencing, e.g. Trainor, Anal. Chem., 62: 418-426 (1990), to the diagnosis of genetic disease, e.g. Watkins, Biotechniques, 6: 310 -319 (1988), to the analysis of carbohydrate mixtures, e.g. Jackson, et al., Electrophoresis, 12: 94 -96 (1991).
Typically, analytical electrophoresis is performed in a "slab" format. The technique of slab gel electrophoresis is well known in the art of biochemistry and molecular biology, e.g. Rickwood et al., eds., Gel Electrophoresis of Nucleic Acids: A Practical Approach, IRL Press, New York, (1990). In slab gel electrophoresis, an electrophoretic separation medium, typically a crosslinked gel, is placed between two rectangular non-conducting plates, e.g. glass plates, which are separated by two side spacers located at the side edge regions of the plates, thereby forming a "gel sandwich". The side spacers ensure that the distance between the glass plates is uniform across the gel, thereby ensuring a uniform gel thickness. The top and bottom edges of the gel sandwich are immersed in buffer solutions which are contained in top and bottom buffer reservoirs. Top and bottom electrodes are mounted within top and bottom buffer reservoirs. The purpose of the buffer solutions is to provide electrical contact between the top and bottom electrodes and the top and bottom edges of the gel sandwich. Sample is loaded onto the top of the gel, and an electrical potential is applied across the gel, causing the charged sample to move through the gel. Automated slab-gel electrophoresis systems additionally include a real-time-scanning fluorescence detector, e.g. Hunkapiller et al., U.S. Pat. No. 4,811,218 to detect multiple fluorescently labeled samples as they travel through the gel. In order to collect data from multiple lanes during electrophoresis, the optical detector system is scanned across the width of the gel in a direction perpendicular to the direction of migration of the fluorescently labeled samples.
It is important to the proper functioning of the slab gel electrophoresis process that the side spacers remain in contact with the electrophoresis gel throughout the analysis, i.e. that no voids or channels appear between the side spacers and the gel. Such voids can lead to a variety of problems including electrical short circuits, non-homogenous electric fields, destruction of the gel, and, in some extreme cases, fire. The present invention is directed towards apparatus and methods which ensure intimate contact between the side spacer and the electrophoresis gel, thereby reducing the likelihood of void formation and the resulting complications.